(a) Technical Field
The present invention relates to a catalyst for Fischer-Tropsch synthesis (FTS), a method for preparing same and a method for preparing liquid hydrocarbons from a syngas using same.
(b) Background Art
In general, cobalt-based catalysts are mainly used in preparation of liquid hydrocarbons from a syngas through Fischer-Tropsch synthesis (FTS). The cobalt-based catalyst is known to have high carbon monoxide conversion, long life and superior hydrocarbon selectivity due to low CO2 production rate. However, because the cobalt-based catalyst favors production of methane predominantly at high temperatures of 300° C. or above, design of the catalyst for control of local temperature increase using a catalyst-bed is of importance. Due to this problem and in terms of cost reduction and enhancement of activity, a support having thermally and chemically stable pores and having a large surface area such as alumina, silica, titania, etc. is used and an active component is dispersed thereon, although heat transfer effect is lower.
According to the Anderson-Schulz-Flory (ASF) distribution, straight-chain hydrocarbons are mainly produced by the FTS reaction. In case of high-boiling-point hydrocarbons, carbon deposition may be predominant at hot spots over product desorption, thereby quickly deactivating the catalyst [Chemical Reviews 107 (2007) 1692]. Accordingly, in order to enhance dispersion of the active component of cobalt and to inhibit carbon deposition, a support having a large surface area, such as alumina, silica or titania described above, is often surface-treated to improve catalytic activity by controlling the particle size of supported cobalt [Journal of American Chemical Society, 128 (2006) 3956]. As an example of such support surface treatment, a method of inhibiting carbon deposition on the surface of a catalyst prepared using a silica-alumina support having a bimodal pore size distribution by enhancing the speed of transportation of high-boiling-point hydrocarbons produced during the FTS reaction is reported [US Patent Application Publication No. 2005/0107479 A1].
Meanwhile, a method of modifying the surface of a silica support using an enhancer such as zirconium in order to enhance reducibility of cobalt and improve selectivity for high-boiling-point hydrocarbons by inhibiting adsorption of FTS products is also reported [Journal of Catalysis, 185 (1999) 120].
As for methods of performing the FTS reaction using silicon carbide (SiC) as a support, it is reported that a superior catalytic activity is achieved when the FTS reaction is performed using a SiC support having superior heat transfer effect prepared by mixing with an inorganic material (e.g., silica sol) and using cobalt as an active component [U.S. Pat. No. 5,710,093]. It is also reported that a cobalt-based FTS catalyst prepared by coating an alumina sol on a silicon carbide foam having mesopores has superior catalytic activity because of improved mass transport effect owing to the large-sized pores of the silicon carbide foam [Applied Catalysis A: General, 397 (2011) 62]. All of these preceding researches use cobalt-based catalysts prepared by using the silicon carbide support having superior heat transfer property and enhancement of catalyst stability through improved cobalt dispersion and controlled metal-support interaction between the cobalt active component and the alumina support or improvement of catalytic activity through introduction of a bimodal pore size distribution and a method for preparing such a catalyst have not been presented yet.
The present invention aims at presenting a method for inhibiting deactivation of a catalyst using a silicon carbide support caused by deposition of hydrocarbon compounds by maximizing heat transfer effect and thus controlling hot spots as well as a method for preparing a support having a bimodal pore size distribution by controlling the pores of an alumina-coated silicon carbide support and thereby improving catalytic activity through enhanced cobalt dispersion and ensuring long-term catalyst stability through controlled interaction between cobalt and the support.
Throughout the specification, a number of publications and patent documents are referred to and cited. The disclosure of the cited publications and patent documents is incorporated herein by reference in its entirety to more clearly describe the state of the related art and the present invention.